To determine the base sequence of DNA or RNA, a method based on electrophoresis has been mainly used. This method includes the steps of preparing a cDNA fragment sample synthesized in advance via a reverse transcription reaction of a DNA fragment or a RNA sample for sequencing, for which a dideoxy reaction based on the well-known Sanger method is performed, followed by electrophoresis, thus measuring its molecular weight separation/expansion pattern for analysis. Meanwhile, a recently developed method called a next-generation DNA sequencer performs the steps of immobilizing a large number of DNA fragments as a sample to a substrate and determining information on the sequence of these fragments in parallel.
Such a next-generation DNA sequencer places a lot of beads, to which DNA fragments as a sample are immobilized, in a flow cell as a reaction field. Then, a reagent is supplied to the flow cell, and fluorescent signals generated due to an elongation reaction of bases are detected, based on which the base sequence of the sample is analyzed. Many of these next-generation DNA sequencers use a solution sending system including a tube and a valve to supply a reagent. Specifically, the system includes a tube making up a supply passage of each reagent and another tube connected to a flow cell as well as a valve placed therebetween, and switches the valves, thus supplying a desired reagent to the flow cell.